weakref

Weakref provides a cheap Copy + 'static reference type Ref<T>. You can pass it anywhere almost effortlessly, then check if the reference is alive at runtime. The single owner Own<T> increments a global per-object generation counter when dropped.

This is inspired by https://verdagon.dev/blog/surprising-weak-refs, although the implementation has changed quite a bit vs what is used in Vale.

Basic Usage

use weakref::{Own, Ref, pin, refer};

let data = Own::new(vec![1, 2, 3]);

std::thread::spawn(move || {
    match refer!(data).get(&pin()) {
        Some(data) => println!("{data:?} is still alive!"),
        None => println!("data got dropped!"),
    }
});

drop(data);

Performance Characteristics

Each Own/Ref is 24 bytes on the stack, and globally allocates a single 8-byte generation counter. The counter can never be freed (since it must remain accessible to Ref forever) but can be reused indefinitely. Access requires pinning the thread with crossbeam_epoch and atomically loading the generation counter to check if it matches. Dropping Own requires pinning the thread, deferring the destructor, incrementing the generation counter, and pushing it to a queue to be reused.

Weakref has broadly similar performance as Arc, except with totally free Ref copies. As of version 0.1.0 my benchmarks show Own+Ref behind but with plenty of room still for optimization.